Drawbridge.



2 SHEETS-SHEET 1.

Patented Nov. 11, 1913.

B. LESLIE.

DRAWBRIDG'E. APPLIGATION FILED JAN. 24.1912.

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B. LESLIE. DRAWBRIDGB. APPLICATION FILED JAN. 24,1912.

v Patented Nov. 11, 1913.

2 SHEETS-SHEET 2.

:enADroaD LESLIE, or LoNDoN, ENGLAND.

1 Dnawisainen.

'Specification of Letters Patent.

Patented Nov. 1 1, 1913.

Application filed January 24, 1912. 4Serial No. 673,102.

To all whom t may concern:

Beit known that I, BRADFORD LESLIE,K. G. l. E., a subject of the King of Great Britain, residing in London, England, andwhose post-office address is 5 Chester Grate, Regents Park, in the county of London, England, engineer, have invented a certain new and useful Improvement in a Drawbridge, of which the following is a specification.V

lSuspended folding drawbridges hitherto constructed have always been made with the inner leaf articulated to the abutment and with the points of suspension of the leaves at the ends thereof. This construction has the disadvantage that the whole weight of `the leaves has to be lifted and the consumption of power is considerable. To overcome this objection the inner leaf has been pivoted to the abutment at a point between its ends so as to form a lever, the free end of which carries a counterweight. ln this case there is the disadvantage that the rigidity of the girder composed of the two leaves is considerably reduced;V moreover the total length of the bridge has to be'increased by the portion extending beyond the abutment over the shore.

The present invention provides a suspended drawbridge wherein when the bridge is being opened or closed the two leaves balance each other substantially completely, in such lmanner that their common center of gravity travels inward horizontally, if there is'suiiicient clearance above the 'waterz or ifi there is not suflicientY clearance to avoid nny mersion of the leaves in the water when they vare in thel folded position,` the balance mayl 'such that when the' clearance between the road` or 'rail'and the water is not less in depth thansa'y 25-per cent.v of the length of the bridge or the half-span the leaves may be folded or 'extended without substantial alteration of thelevel of their common center of'gravity. When the clearance is less than this, it becomesnecessary to raise the common center-off gravity when raising the bridge, yby an amount inversely. proportional tothe clearance available. The leaves 4are supported by chains from pillars crthe like, on the abutment without other attachment to the abutment; the points of suspension being so located that the portions of the leaves external to such pointsV partially'ba-lanc'e the portions between LJthe points; the free ASend.

of theinn'erleaf rests -against the abutment but freethereof, so that-as soon as the locklng device, which holds up this end when the bridge is-closed, has been withdrawn, this innerend travels downward, thus Yraising the hinge that connects the two leaves'V above theline-of thrust of the compound-girder and makin-git possible `to lift'the leavesby asm-all expenditure of power.

The accompanying diagrams illustrate the invention. Y

Figure 1 representsya side 4elevation of the half-span of a bridge the height of which above the water level .et-A is more than 25 per cent. ofthe length of the half-span, and F ig. 2 a side elevation of the half-spanwhen the height is less than this. Fig. 3 isan en` larged view of the lower right'hand portion of Fig. l. e

Referring to Fig. l, the'platform; of the bridge is carried `between a pair of side girders each composed of two 'substantially 'equal parts "a, a, the lower members of the girders constituting these parts, which may conveniently be called -outer and' inner leaves respectively, being hinged together asat a2. When thepleaves are extended as shown in the drawing the upper members of the girders abut against cach other. The girders are suspended by chains `Z) b in a suitable `manner from a pair of pillars or other ap propriate support c erected .on the abutment and properly stayed according to well-known engineering practice, These chains support the dead-weight of the drawbri'dge as well as the live load, and when extended the drawbridge forms'the bottom member of asuspended cantaliver.

When the'leaves are-extended their centers of' gravity are between the points of sus pensionofathe leavesfrom chains b b', the distances of the'sepoi-ntsfroin the centers of gravitydeperrding on the height of lift refquired. The horizontal Vcomponent o`fV the force `sustaining the extended leaves is a pressure transmitted through the girders to the abutment. The lline of this thrust -is -above the hinge` 0.2,' in order to fold the leaves the hinge must be raised above the line of pressure. For the purpose, the inner ends of thegirders carry` rollers d which, in the` extended position of the leaves, rest against 'the upper end of concavely curved roller paths e made in the abut-ment or otherwise provided. The'curvature of the roller ,paths is such that the horizdnai thrust. would cause the roller to travel down the path were it not prevented by a suitable lock, such as the arm f of a shaft g this arm extends beneath the inner end of the inner leaf a and supports the latter. When it is desired to fold the leaves, the shaft g is turned, it-

may be by means of a worm 7u and a toothed Vapplying sufficient lifting force to balance theexcess weight of the leaves at the hinge and thus to cause the roller to continue its movement down the path. Any convenient mode of applying this force may be adopted. In Fig. l there is shown an oscillating derrick 7c stepped in fro-nt of the support 0,' the end of this derrick is connected on the one hand with a toothed segment -Z and on the other hand, by means of a spar 7c', with the hinged end of the leaf a. kThe segment Z is 'engaged by a pinion m driven, for instance,

by an electric motor; the segment carries a pair of wheels a which travel on a fixed path 0. Y v

Y It isan object tokeep the two leaves balanced as far as possible during the operation of folding or extending, and to this end the leaves should remain throughout the operation at substantially the same inclination to the vertical through hinge a2. The point of suspension of the chain b to the supporting pillar is such that when the leaves are completely folded, as indicated in dotted lines,

the chain is vertical, in this position it carries the weight of both leaves and the roller d is at the bott-om of its curved path. vThe inclination of the leaf a during the operation of folding depends on the rotation of the leaf about its point o-f suspension to the chain lasv this swings into the vertical position and roller d travels down its path. To preserve the desired inclination of the leaf a, there isprovided a collapsible strut D normal to the leaf and supporting the chain b at a certain distance from the attachment of the chain to the leaf. The length and position of the strut are such that during the folding of the leaves and also whenv these are in the vertical, folded position, the chain b continues to carry the weight of leaf a and finally counteracts the tendency ofthe folded leaves to fall outward consequent on y the-centerof gravity being outside the point -of suspension of the inner chain. `When the Vleaves have'attained the vertical, folded position, the inner leaf a is caught by a catch and the other part to the girder a; as a means for collapsing the strut, the latter part may carry a toothed sector 1 engaging a pinion s adapted to be turned by a handv wheel.

To extend the leaves, the strut 79 is opened and the locking hook g raised. The power being disconnected, the leaves then fall into the position of equilibrium, that is until the hinge a2 approaches the line of horizontal thrust. Then the raising of lever arm f brings the leaves into the fully extended position. 0r the power may be applied through the spar lo for pressing the leaves into the extended position.

In Fig. 2 the general arrangement is similar to that described with regard to Fig. 1 and the same reference letters are used to indicate like parts. As, however, the bridge is much nearer the water and the leaves must be lifted clear of the water, the points of suspension from the chains Z), b must be correspondingly farther from the center of gravity of the leaves. This entails a much larger proportion of unbalanced weight at the hinge a2 and the common center of gravity has to be raised considerably instead of moving in a substantially horizontal line. In order to enable the bridge to be operated with about the same expenditure of power as in the case of Fig. l the aforesaid unbalanced weight is counterbalanced by weight t connected by link u with the segment l and provided `with wheels to travel on the ineline e. The curved path e is correspondingly shorter than that shown in Fig. 1. It may be added that the curvature of this path may be experimentally determined for each case. When the two leaves constitute the whole span of the bridge, part of the live load may be carried by the opposite abutment.

l.Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim:-

l. A folding drawbridge comprising an abutment, pillars on the abutment, an inner leaf having its inner end resting against but separate from the abutment, and an outer leaf hinged to the outer end of the inner leaf, the said leaves being suspended from the said pillars without other pivotal attachment to the abutment and at points intermediate of their ends, in a manner to allow them to turn about their points of suspension.

2. AV folding drawbridge comprising an abutment, pillars on the abutment, an inner leaf having its inner end resting against but separate from the abutment, and an outer leaf hinged to the outer end of the inner leaf, the said leaves being suspended from the said pillars without other pivotal attachment to the abutment, the points of suspension being intermediate of the ends of the leaves and in such positions that the portions of the leaves external to the said points partially balance thev portions between the points.

3. A folding drawbridge comprising two leaves, each hinged to the other at one end, an abutment, pillars on the abutment, chains suspending the outer leaf from the said pillars and chains suspending the inner leaf from the said pillars, lthe points of attachment of the said chains to the said leaves being so located that the portions of the leaves external to the points partially balance the portions between the points, means for locking the said leaves in extended end to end position, means for releasing the said means, means for applying power to fold the bridge and means for reducing the effectivelength of the chains suspending'the outer leaf correspondingly as the leaf folds against the inner leaf.

el. A folding drawbridge comprising two leaves, each hinged to the other at one end, an abutment, pillars on the abutment, chains suspending the outer leaf from the said pillars and chains suspending the inner leaf from the said pillars, the points of attachment of the said chains to the said leaves being so located that the portions of the leaves external to the point-s partially balance the portions between the points, means for locking the said leaves in extended end toend position, means for releasing the said means, means for applying power to fold the bridge, andf struts pivoted at one end to the chains suspending the outer leaf and attached at the other ends to points in the outer leaf between the points of attachment ofl its suspending chains and the hinged end of the leaf.

55A folding drawbridge comprising two leaves, each hinged to the other at one end,

an abutment, pillars on Vthe abutment, chains suspending the outer leaf from the said pillars and chains suspending the inner leaf from thesaid pillars, the points of attachment o-f the said yChains to the said leaves being so located that the portions of the BRADFORD LESLIE.

Witnesses:

J osnrH MILLARD, vWALTER I. SKIRTEN.

Copies of this patent may be obtained for ive cents each, by addressing the Commissioner of Patents, Washington, D. C. 

